Double-throw miniature electromagnetic microwave switches with latching mechanism

ABSTRACT

Miniature double-throw electromagnetic microwave switches are disclosed in this invention. In one embodiment a switch comprising an input transmission line, a first movable cantilever with a first permanent magnetic film and connecting to a first output transmission line, a second movable cantilever with a second permanent magnetic film and connecting to a second output transmission line is provided. In another embodiment, a latching function is provided to a miniature double-throw electromagnetic microwave switch by adding a permanent magnetic film to said input transmission line. In yet another embodiment, a third non-movable cantilever with a permanent magnetic film on top is added to said miniature double-throw microwave latching switch to enhance the latching mechanism. In yet another embodiment, a miniature double-throw microwave switch is disclosed where at least one recess contact region for each movable cantilever is provided to reduce the effects of unwanted particles and to reduce the contact resistance by increasing contact pressure. In still another embodiment, a miniature double-throw microwave switch having non-symmetrical movable cantilevers and transmission lines, with tapered or rounded corners is given. This is done in order to minimize the reflection and losses of propagating microwaves or millimeter waves.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates generally to miniature electromagneticswitches for microwave systems. More specifically, the invention relatesto a miniature double-throw electromagnetic switch for operation inmicrowave or millimeter wave frequencies.

[0003] 2. Description of the Prior Art

[0004] Switches are basic building blocks of communication electronicsand are widely used for telecommunications applications such as signalrouting, redundancy switching, impedance matching networks andadjustable gain amplifiers. Mechanical relay, PIN diode and FET are thecommon microwave switches. Mechanical relays offer the benefits of lowinsertion loss, large off-state isolation, high linearity and high powerhandling capabilities. However, they consume a significant amount ofpower and are bulky, heavy and slow. Semiconductor switches such as PINdiode and FET provide much faster switching speed and smaller size andweight but are inferior in insertion loss, isolation, linearity andpower handling capabilities than mechanical relays.

[0005] Microwave switches providing the advantageous properties of boththe mechanical relay and semiconductor switch are then highly desirable,especially for space, airborne and mobile telecommunicationsapplications. Micromachining technologies promise to enable thefabrication of such switches, i.e., switches with the high microwaveperformance of mechanical switches but also with the small size, weightand power consumption of semiconductor switches. Furthermore,conventional microelectronics fabrication processes are usually used formicromachining, making the integration of such miniature switches withother active electronics possible.

[0006] In U.S. Pat. No. 6,016,092 entitled “Miniature ElectromagneticMicrowave Switches and Switch Arrays” filed on Aug. 8, 1998 by C. X.Qiu, L. S. Yip and Y. C. Shih, single-pole single-throw microelectromagnetic switches in a coplanar waveguide, a microstrip orstripline form were described. A double-throw switch in a stripline formwas also described. More recently, in U.S. patent application Ser. No.09/400,256 entitled “Double-throw Miniature Electromagnetic MicrowaveSwitches” filed on Sep. 21, 1999 by the same inventors of the above U.S.patent, double-throw micro electromagnetic switches in a microstrip formand a coplanar waveguide form and with controlled magnetization aredisclosed. These single-pole double-throw switches are useful to thefabrication of microwave modules, which require a plurality of switchesfor operation at microwave or millimeter wave frequencies.

[0007] Two schematic views of a prior art of a miniature double-throwelectromagnetic switch (20) disclosed in U.S. patent application Ser.No. 09/400,256 entitled “Double-throw Miniature ElectromagneticMicrowave Switches”, filed on Sep. 21, 1999 by L. S. Yip, C. X. Qiu andY. C. Shih, hereinafter called Double-throw Switch A, are shown in FIGS.1(a) and 1(b). FIG. 1(a) shows a schematic top view of the Double-throwSwitch A (20) and FIG. 1(b) shows the schematic cross-sectional view ofthe switch (20) taken along line A-A′ in FIG. 1(a). The double-throwswitch A (20) is fabricated on a dielectric substrate (21) with a groundplane (22 in FIG. 1(b)) deposited on backside of the dielectricsubstrate (21). An input microstrip line (23 a) and a first outputmicrostrip line (25) are deposited on a front side of the dielectricsubstrate (21). It is seen that the input microstrip line (23 a) and thefirst output microstrip line (25) are aligned in such a way that acontinuous microstrip line can be formed when the two are connectedelectrically. The input microstrip line (23 a) and the first outputmicrostrip line (25) are separated by a gap (24) having a length,(L_(g)). A first cantilever (23 b) with a length (26) is deposited overthe gap (24) (see FIG. 1(b)). A layer of permanent magnetic material(27) is deposited on part of the first cantilever (23 b). A secondoutput microstrip line (28) having a second cantilever (29) is depositedso that the second cantilever (29) is suspended over the firstcantilever (23 b). The second output microstrip line (28) may bedeposited on the same dielectric substrate (21) with the inputmicrostrip line (23 a) and the first output microstrip line (25), or ona different dielectric substrate. The second cantilever (29) overlapspart of the first cantilever (23 b) in region without the magnetic film(27) so that when the first cantilever (23 b) is pushed upwards, aleading portion of the first cantilever (23 b) can make electricalcontact with the second cantilever (29). The overlap between the firstcantilever (23 b) and the first output microstrip line (25) is (36)whereas the overlap between the first cantilever (23 b) and the secondcantilever (29) is (37). A layer of dielectric material (22′) such asSiO₂ or polyimide is applied on the ground plane (22). A miniatureelectromagnetic coil (30) is deposited or attached to the dielectricmaterial (22′). Width (31) of the input microstrip line (23 a) and thefirst output microstrip line (25) is selected to be substantially equalto the width (32) of the second output microstrip line (28). Values of(31) and (32) are determined by the thickness (33, in FIG. 1(b)) of thedielectric substrate (21), the dielectric constant, and the centralfrequency of the microwave signals to transmit for low loss operation.The second output microstrip line (28) may be arranged so that it makesan angle of roughly 90 degrees with respect to the input microstrip line(23 a) and the first output microstrip line (25).

[0008] The operation of the Double-throw Switch A (20) is as follows.When no current is applied to the miniature electromagnetic coil (30)(I=0), no magnetic force is applied to the first cantilever (23 b) andthe first cantilever (23 b) is in a normal position in between the firstoutput microstrip line (25) and the second cantilever (29) of the secondoutput microstrip line (28). When a positive current (I>0) is applied tothe miniature electromagnetic coil (30), so that the direction of themagnetic field (B_(e)) induced is substantially parallel and opposite tothe magnetic moment (B_(m), in FIG. 1(b)) of the permanent magnetic film(27), an attraction force will be caused on the first cantilever (23 b).When the current (I) exceeds a pull-down threshold or when the force issufficiently large, the first cantilever (23 b) will be deformed so thatthe first cantilever (23 b), attaching to the input microstrip line (23a), will get in contact with the first output microstrip line (25).Microwave signals applying to the input microstrip line (23 a) will beallowed to reach the first output microstrip line (25). Since there isno electrical contact between the first cantilever (23 b) and the secondcantilever (29), which is connected to the second output microstrip line(28), the incoming microwave signals will not reach the second outputmicrostrip line (28). When the current (I) through the miniatureelectromagnetic coil (30) is reversed, so that the direction of themagnetic field (B_(e)) induced is substantially parallel and along themagnetic moment (B_(m)) of the permanent magnetic film (27), a repulsionforce will be caused on the first cantilever (23 b). When the reversecurrent (I) exceeds a push-up threshold or the repulsion force issufficiently large, the first cantilever (23 b) will be pushed away fromthe first output microstrip line (25) and eventually get in contact withthe second cantilever (29) connected to the second output microstripline (28). Microwave signals supplying to the input microstrip line (23a) will not be allowed to reach the first output microstrip line (25).Since there is electrical contact between the first cantilever (23 b)and the second cantilever (29), the incoming microwave signals willreach the second output microstrip line (28). It is consequently clearthat the Double-throw Switch A (20) requires continuous supply ofcurrent (I) to the micro-coil (30) in order to obtain reliableoperation, at least for one of the two operation states.

[0009] A second miniature double-throw microwave switch disclosed inU.S. patent application Ser. No. 09/400,256 filed on Sep. 21, 1999 by L.S. Yip, C. X. Qiu and Y. C. Shih, hereinafter called Double-throw SwitchB, which is related to this invention is shown in FIGS. 2(a) and 2(b).FIG. 2(a) shows a top view of the Double-throw Switch B (70) on adielectric substrate (71). FIG. 2(b) is the schematic side view of theswitch (70) taken along line D-D′ in FIG. 2(a). The double-throw switch(70) contains a first cantilever (72) and a second cantilever (73). Thelength of the first cantilever (72) and the second cantilever (73) arechosen to be the same and is given by (26). A first permanent magneticfilm (74) is deposited on the first cantilever (72) whereas a secondpermanent magnetic film (75) is deposited on the second cantilever (73).The first cantilever (72) overlaps part of a first output microstriptransmission line (76) whereas the second cantilever (73) overlaps partof a second output microstrip transmission line (77). Both cantilevers(72, 73) are connected to an input microstrip transmission line (78).Hence one end of the input microstrip transmission line (78) has a firstcantilever (72) and the other end has a second cantilever (73). Width(76 a) of the first output microstrip transmission line (76) is made tobe substantially equal to the width (77 a) of the second outputmicrostrip transmission line (77) and the width (78 a) of the inputmicrostrip transmission line (78). Values of (76 a), (77 a) and (78 a)for low loss operation are determined by the thickness (84, in FIG.2(b)) of the dielectric substrate (71), the dielectric constant, and thecentral frequency of the microwave signals to transmit.

[0010] As seen in FIG. 2(b), the overlap between the first cantilever(72) and the first output microstrip line (76) is (86) and the overlapbetween the second cantilever (73) and the second output microstrip line(77) is (87). The first output microstrip line (76) and the inputmicrostrip line (78) are separated by a gap (88) whereas the secondoutput microstrip line (77) is separated from the input microstrip line(78) by another gap (89). Also seen in FIG. 2(b), a miniatureelectromagnetic coil (81) is deposited or attach to a dielectricmaterial (82), which is deposited on the ground plane (83).

[0011] The operation of the Double-throw Switch B (70) is as follows.Since only one miniature electromagnetic coil (81) is used to actuatethe two cantilevers (72, 73), the magnetic polarizations (B_(m), B_(m)′)on the two permanent magnetic films (74, 75) must be different. When themagnetic polarizations (B_(m), B_(m)′) are different, preferablyopposite, and with a positive current (I) applied to the miniatureelectromagnetic coil (81), the magnetic field (B_(e)) created willinduce attraction force on the second cantilever (73) and a repulsionforce on the first cantilever (72), causing contact of the secondcantilever (73) with the second output microstrip line (77) whilecausing an open between the first cantilever (72) and the first outputmicrostrip line (76). Hence microwave signals incident from the inputmicrostrip line (78) will be allowed to go through the second cantilever(73) to reach the second output microstrip line (77). Since there is noelectrical contact of the input microstrip line (78) with the firstoutput microstrip line (76), microwave signals will not be coupled fromthe input microstrip line (78) to the first output microstrip line (76).When the current (I) applied to the miniature electromagnetic coil (81)is reversed, the magnetic field (B_(e)) from the miniatureelectromagnetic coil (81) will be inverted to induce a repulsion forceon the second cantilever (73) and an attraction force on the firstcantilever (72), causing contact between the first cantilever (72) andthe first output microstrip line (76) while causing an open between thesecond cantilever (73) and the second output microstrip line (77).Hence, when the current (1) is inverted, microwave signals incident fromthe input microstrip transmission line (78) will be allowed to gothrough the first cantilever (72) to reach the first output microstripline (76). Since there is no electrical contact between the secondcantilever (73) and the second output microstrip transmission line (77),microwave signals will not be coupled from the input microstriptransmission line (78) to the second output microstrip transmission line(77).

[0012] Although the Double-throw Switch B (70) may operates at amoderate microwave frequencies, when the first cantilever (72) isactuated to make contact with the first output transmission line (76)the open second cantilever (73) connected to the input microstriptransmission line (78) will act as an antenna and result in unwantedreflection and losses of the incident microwave signals at higherfrequencies. This is because the length (26) of the second cantilevercan't be made too small compared with wavelength of the microwavessignal at high frequencies.

SUMMARY OF THE INVENTION

[0013] The present invention allows the fabrication of miniatureelectromagnetic double-throw switches based on the micro-machiningtechnologies to minimize RF losses and to increase the RF frequencies ofoperation. The present invention also allows the switches to havelatching mechanism to minimize the power consumption of the double-throwswitches.

[0014] In one embodiment of this invention, a double-throw miniaturemicrowave switch with a dielectric substrate, an input transmissionline, a first movable cantilever and a second movable cantilever eachwith a permanent magnetic film is provided. Said first movablecantilever forms part of a first output transmission line whereas saidsecond movable cantilever forms part of a second output transmissionline. When actuated by a magnetic field in one direction, said firstmovable cantilever moves downwards to cause contact between said inputtransmission line and said first output transmission line whereas saidsecond movable cantilever moves upwards to isolate said second outputtransmission line from said input transmission line. When the directionof said actuation magnetic field is reversed, said first movablecantilever moves upwards to cause an isolation between said inputtransmission line and said first output transmission line whereas saidsecond movable cantilever moves downwards to cause contact between saidinput transmission line and said second output transmission line.

[0015] In another embodiment, a double-throw miniature microwave switchwith recess contact regions is provided. The presence of un-wantedparticles on the substrate is unavoidable and those under the movablecantilevers in a switch may increase the contact resistance and reducethe contact pressure. By creating at least one recess contact region foreach movable cantilever, the effect of said unwanted particles can bereduced and the contact pressure can be increased to give rise to areduced contact resistance.

[0016] In yet another embodiment, a double-throw miniature microwaveswitch, having non-symmetrical movable cantilevers and transmissionlines with tapered or rounded corners is given. Sharp corners intransition between the input transmission line and the outputtransmission line are eliminated in this switch to minimize thereflection and losses of propagating microwaves or millimeter waves.

[0017] In yet another embodiment, a double-throw miniature microwaveswitch with latching is given. Said switch consists of a dielectricsubstrate, an input transmission line, a first output transmission linewith a first movable cantilever and a second output transmission linewith a second movable cantilever. At least part of said inputtransmission line, part of said first movable cantilever and part ofsaid second movable cantilever are covered with permanent magneticfilms. Magnetization of said permanent magnetic films is controlled toallow latching in one state to occur when said switch is actuated sothat said first movable cantilever moves towards said input transmissionline, arising from an external magnetic field. Latching between saidfirst movable cantilever and said input transmission line occurs due toa magnetic attracting force between said permanent magnetic films insaid first movable cantilever and in said input transmission line.Hence, microwaves from said input transmission line is allowed topropagate to said first output transmission line but not allowed topropagate to said second output transmission line. Latching will alsooccurs in another state when said switch is actuated so that said secondmovable cantilever moves towards said input transmission line, arisingfrom a reversed external magnetic field. Latching between said secondmovable cantilever and said input transmission line occurs due to amagnetic attracting force between said permanent magnetic films in saidsecond movable cantilever and in said input transmission line. In thiscase, microwave signals from said input transmission line will beallowed to propagate to said second output transmission line but willnot be allowed to propagate to said first output transmission line.

[0018] In yet another embodiment, a double-throw miniature microwaveswitch with latching is given. Said switch consists of a dielectricsubstrate, an input transmission line, a first output transmission linewith a first movable cantilever, a second output transmission line witha second movable cantilever and a third non-movable cantilever forlatching. At least part of said input transmission line, part of saidfirst movable cantilever, part of said second movable cantilever andpart of said third non-movable cantilever are covered with permanentmagnetic films. Magnetization of said permanent magnetic films iscontrolled to allow latching in one state to occur when said switch isactuated so that said first movable cantilever moves towards said inputtransmission line, arising from an external magnetic field. Latchingbetween said first movable cantilever and said input transmission lineoccurs due to a magnetic attracting force between said permanentmagnetic films in said first movable cantilever and in said inputtransmission line. Magnetization of said permanent magnetic films isalso controlled to allow latching in this state to occur when saidswitch is actuated so that said second movable cantilever moves towardssaid third non-movable cantilever, arising from said external magneticfield. Latching between said second movable cantilever and said thirdnon-movable cantilever occurs due to a magnetic attracting force betweensaid permanent magnetic films in said second movable cantilever and insaid third non-movable cantilever. Hence, microwaves from said inputtransmission line is allowed to propagate to said first outputtransmission line but not allowed to propagate to said second outputtransmission line. Latching will also occurs in another state when saidswitch is actuated so that said first movable cantilever moves towardssaid third non-movable cantilever and gets latched, whereas said secondmovable cantilever moves towards said input transmission line and getslatched. In this case, microwave signals from said input transmissionline will be allowed to propagate to said second output transmissionline but will not be allowed to propagate to said first outputtransmission line.

[0019] In still another embodiment, a double-throw miniature microwaveswitch with latching mechanism and a smooth transition region is given.Said switch consists a dielectric substrate, an input transmission linewith a movable cantilever, a first output transmission line and a secondoutput transmission line with a non-movable cantilever. At least part ofsaid movable cantilever, said non-movable cantilever and said firstoutput transmission line are covered with permanent magnetic films.Magnetization of said permanent magnetic films is controlled to allowlatching in one state to occur when said switch is actuated so that saidmovable cantilever moves towards said first output transmission line,arising from an external magnetic field. Latching between said movablecantilever and said first output transmission line occurs due to amagnetic attracting force between said permanent magnetic films in saidmovable cantilever and in said first output transmission line. Hence,microwaves from said input transmission line is allowed to propagate tosaid first output transmission line but not allowed to propagate to saidsecond output transmission line connecting to said non-movablecantilever. Latching in another state will be allowed to occur when saidswitch is actuated so that said movable cantilever moves towards saidnon-movable cantilever connecting to said second output transmissionline, arising from a reversed external magnetic field. Latching betweensaid movable cantilever and said non-movable cantilever occurs due to amagnetic attracting force between said permanent magnetic films in saidmovable cantilever and in said non-movable cantilever connecting to saidsecond output transmission line. In this case, microwave signals fromsaid input transmission line will be allowed to propagate to said secondoutput transmission line but will not be allowed to propagate to saidfirst output transmission line. Since sharp corners in the transitionregion between the input transmission line and the output transmissionlines are eliminated in this switch, the reflection and losses ofpropagating microwaves or millimeter waves are minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1(a) A schematic top view of a prior art showing theDouble-throw Switch A (20) fabricated on a dielectric substrate. (b) Aschematic cross-sectional view of the prior art double-throw microwaveswitch (20) taken along the line A-A′ in FIG. 1(a).

[0021]FIG. 2(a) A schematic top view of a prior art showing theDouble-throw Switch B (70) containing a first cantilever with a firstpermanent magnetic film and a second cantilever with a second permanentmagnetic film and (b) a schematic cross-sectional view of the prior artminiature Double-throw Switch B (70) taken along the line D-D′ in FIG.2(a).

[0022]FIG. 3(a) A schematic top view of a double-throw miniaturemicrowave switch (100) containing an input transmission line, a firstcantilever connected to a first output transmission line with a firstpermanent magnetic film, and a second cantilever connected to a secondoutput transmission line with a second permanent magnetic film. (b) Aschematic cross-sectional view of the switch (100) taken along the lineE-E′ in FIG. 3(a).

[0023]FIG. 4 Schematic cross-sectional views of the double-throwminiature microwave switch (100) illustrated in FIG. 3, demonstrate theswitch in actuation, (a) for the case when an actuation current isapplied to the electromagnet, the first cantilever is pulled down tomake electrical contact with the input transmission line and the secondcantilever is pushed up and (b) for the case when an actuation currentwith an opposite direction is applied to the electromagnet, the secondcantilever is pulled down to makes electrical contact with the inputtransmission line and the first cantilever is pushed up.

[0024]FIG. 5 Schematic cross-sectional views of the double-throwminiature microwave switch (100) in actuation, (a) shows the case whenun-wanted particle present between the first cantilever and thesubstrate and (b) illustrates the case when unwanted particle presentbetween the first cantilever and the input transmission line, resultingin electrical contact breaking between the first cantilever and theinput transmission line.

[0025]FIG. 6(a) shows a schematic top view of a double-throw miniaturemicrowave switch having a recess region on a first cantilever in theoverlap region between the first cantilever and an input transmissionline. The switch also has a recess region on the second cantilever inthe overlap region of the second cantilever and the input transmissionline to increase the contact pressure and to minimize detrimental effectof the presence of unwanted particles. (b) A schematic cross-sectionalview of the microwave switch taken along the line F-F′ in FIG. 6(a),showing the location and arrangement of the recess regions in thecantilevers.

[0026]FIG. 7(a) A schematic top view of a double-throw miniaturemicrowave switch showing recess regions in a first cantilever both inand outside the overlap region of the first cantilever and the inputtransmission line and recess regions in a second cantilever both in andoutside the overlap region of the second cantilever and the inputtransmission line to increase the contact pressure and to minimizedetrimental effect of the presence of unwanted particles. (b) Aschematic cross-sectional view of the microwave switch taken along theline G-G′ in FIG. 7(a), showing the location and arrangement of therecess regions in the cantilevers.

[0027]FIG. 8(a) illustrates a schematic top view of a double-throwminiature microwave switch having an input transmission line withtapered corners, a first non-symmetrical cantilever and a secondnon-symmetrical cantilever each with a tapered inner corner with theinput transmission line, to minimize reflection and losses ofpropagating microwaves or millimeter waves. (b) A schematic top view ofa double-throw miniature microwave switch having an input transmissionline with rounded corners, a first non-symmetrical cantilever and asecond non-symmetrical cantilever each with a rounded inner corner withthe input transmission line, to minimize reflection and losses ofpropagating microwaves or millimeter waves.

[0028]FIG. 9(a) shows a schematic top view of a double-throw miniaturemicrowave switch (100L) with latching mechanism. The switch contains aninput transmission line with an input permanent magnetic film, a firstmovable output cantilever with a first permanent magnetic film andconnected to a first output transmission line, a second movable outputcantilever with a second permanent magnetic film and connected to asecond output transmission line, a third non-movable cantilever with athird permanent magnetic film. (b) A schematic cross-sectional view ofthe microwave switch taken along the line H-H′ in FIG. 9(a).

[0029]FIG. 10 Schematic cross-sectional views of the double-throwminiature microwave switch (100L), (a) for the case when an actuationcurrent is applied to the electromagnet. The first output cantilever ispulled down to make electrical contact with the input transmission linewhereas the second output cantilever is pushed up to the thirdnon-movable cantilever. (b) Shows the switch in a latching state whenthe current to the electromagnet is disconnected. (c) Shows the casewhen an actuation current with an opposite direction is applied to theelectromagnet and (d) displays the switch in another latching state whenthe current to the electromagnet is disconnected.

[0030]FIG. 11 Schematic cross-sectional views of a double-throwminiature microwave switch (100L′) with latching mechanism, showing thecases (a) when an actuation current is applied to the electromagnet and(b) when the current to the electromagnet is disconnected. The secondoutput cantilever is latched to the input transmission line and thefirst cantilever is in a normal position, forming a latched double-throwmicrowave switch. FIGS. 11(c) and 11(d) show the switch with a differentmagnetization for the permanent magnetic films.

[0031]FIG. 12(a) Schematic top view of a double-throw miniaturemicrowave switch (190) having an input transmission line connected to amovable input cantilever with an input permanent magnetic film, a firstoutput transmission line and a second output transmission line connectedto a second non-movable cantilever, showing a smooth transition region.(b) A enlarged schematic cross-sectional view of the microwave switchtaken along the line J-J′ in FIG. 12(a). FIG. 12(c) shows the switchequipped with latching mechanism and (d) shows the switch completed witha double-sided recess region to increase the contact pressure and tominimize detrimental effect of the presence of the unwanted particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] For microwave applications, the switches used may base onresistive coupling or capacitive coupling. To simplify the description,miniature electromagnetic switches based on a resistive coupling will beused in the following description. It is understood that switches basedon capacitive coupling may as well be constructed and fabricated usingthe structures to be described in this invention. In addition, microwaveswitches in a microstrip transmission line form or a coplanartransmission line form may be used. To simplify the explanation,switches in a microstrip transmission line form will be used for thedescription. It is understood that switches based on the coplanartransmission line form may as well be constructed and fabricated usingthe structures to be described in this invention.

[0033] According to one embodiment of this invention, as shown in FIG.3(a), a double-throw miniature microwave switch (100), hereinaftercalled Double-throw Switch C (100) is constructed on a front side of adielectric substrate (101) with an input transmission line (102) havinga width (102′), a first output transmission line (103) having a width(103′) and a second output transmission line (104) having a width(104′). FIG. 3(b) shows the cross-sectional view of the Double-throwSwitch C (100) taken along the line E-E′ of FIG. 3(a), which gives a topview of the Double-throw Switch C (100). As shown in FIG. 3(b), theDouble-throw Switch C (100) is fabricated on the dielectric substrate(101) with a thickness (101″) having a ground plane (105) deposited on abackside of the dielectric substrate (101). Thickness of the groundplane is in a range from 0.3 μm to 10 μm, dependent on the skin depth ofthe microwave signals to operate. The transmission lines (102, 103,104), with thicknesses (102″, 103″, 104″), are made using metals such asAu, Cu, Ti and W and combinations of them. The widths (102′, 103′, 104′,in FIG. 3(a)) are the same and are selected according to the frequenciesof operation, characteristic impedance, thickness and dielectricconstant of the substrate (101). When an alumina substrate is used, thewidths (102′, 103′, 104′) of the input and output transmission lines(102, 103 and 104) will be approximately equal to the thickness of thealumina substrate.

[0034] As shown in FIG. 3, a first movable cantilever (106) and a secondmovable cantilever (107) are deposited to connect to the first outputtransmission line (103) and the second output transmission line (104)respectively. A first inclined portion (108) raises the first movablecantilever (106) by a separation (110, in FIG. 3(b)) from the inputtransmission line (102) while a second inclined portion (109) raises thesecond movable cantilever (107) by the same separation (110). A firstpermanent magnetic film (111) is deposited on a front surface of thefirst movable cantilever (106) and a second permanent magnetic film(112) is deposited on a front surface of the second movable cantilever(107). The two permanent magnetic films (111, 112) are magnetized insuch a way so that the magnetic polarization of (111, 112) is in thesame direction (as marked by S and N in FIG. 3(b)). The first movablecantilever (106) is fabricated so that the projection of (106) makes anoverlap (113) with the input transmission line (102). Similar, thesecond movable cantilever (107) is fabricated so that the projection of(107) makes an overlap (114) with the input transmission line (102). Theamount of overlaps (113, 114) is determined by the desired minimumparasitic capacitances required for the overlapped regions whencantilevers (106, 107) are not in contact with the input transmissionline (102). It is obvious that for fixed values of separation (110) andwidths (106′, 107′), the parasitic capacitance values are directlyproportional to the amount of overlaps (113, 114). As a general rule,the amount of overlaps (113, 114) is selected to be as small as possibleproviding a good electrical contact between the movable cantilevers(106, 107) and the input transmission line (102) is ensured.

[0035] The operation of the Double-throw Switch C (100) disclosed inFIG. 3 is illustrated in FIG. 4. In FIGS. 4(a) and 4(b), anelectromagnet (120) is placed under the Double-throw Switch (100). Asshown in FIG. 4(a), when a dc current is applied to the electromagnet(120), the magnetic flux generated (121, 122) points away from theelectromagnet (120) at the top of the electromagnet (120). Due to themagnetic flux (121) going through the first permanent magnetic film(111), the first permanent magnetic film (111) will be attracted towardsthe electromagnet (120), so that the leading end of the first movablecantilever (106) will get in touch with the input transmission line(102). Since the magnetization of the two permanent magnetic films (111,112) are in the same direction (pointing from N to S) and the directionof the magnetic flux (122) going through the second permanent magneticfilm (112) is opposite to that experienced by the first permanentmagnetic film (111), the second permanent magnetic film (112) willexperience a repulsion force and the second movable cantilever (107)will be pushed away from the input transmission line (102). Hence,microwave signals applied to the input transmission line (102) will bedirected towards the first output transmission line (103). As shown inFIG. 3(a), the microwave-propagating path including the inputtransmission line (102), the first movable cantilever (106) and thefirst output transmission line (103) has a uniform value for (102′,106′, 103′). Hence, the reflection and losses of propagating microwavescan be minimized.

[0036] When the direction of the dc current to the electromagnet (120)is reversed, the magnetic flux generated (123, 124 in FIG. 4(b)) willreverse. In this case, as shown in FIG. 4(b), the first permanentmagnetic film (111) will experience a repulsion force and the firstmovable cantilever (106) will be pushed away from the input transmissionline (102). Whereas the second permanent magnetic film (112) willexperience an attracting force and the second movable cantilever (107)will be attracted to make contact with the input transmission line(102). Microwave signals applied to the input transmission line (102)will now be directed towards the second output transmission line (104).As shown in FIG. 3(a), the widths (102′, 107′, 104′) of themicrowave-propagating path including the transmission line (102), thesecond movable cantilever (107) and the second output transmission line(104) are uniform. Hence, the reflection and losses of propagatingmicrowaves can be minimized.

[0037] Although Double-throw Switch C (100) with horizontalmagnetization for (111) and (112) are described, it should be noted thata vertical magnetization, similar to Double-throw Switches B (See FIG.2(b)) in prior art, could be used in the Double-throw Switch C (100) aswell. In such a case, the magnetization for the first permanent magneticfilm (111) and the second permanent magnetic film (112) should beopposite to each other so that when the first permanent magnetic film(111) is experiencing an attracting force, the second permanent magneticfilm (112) will experience a repulsing force. Therefore, it isunderstood that Double-throw Switch C (100) with vertical magnetizationsmight as well be constructed and fabricated using the structuresdescribed in this invention.

[0038] During the operation of the Double-throw Switch C (100), certainparticles may be present due to contamination or releasing of particlesfrom the substrate and the packaging materials. FIG. 5(a) shows theeffects of the presence of a particle (130) between the substrate (101)and the first movable cantilever (106) for the Double-throw Switch C(100) illustrated in FIG. 4(a). If the dimension of the particle (130)is greater than the thickness (102″) of the input transmission line(102), then the first movable cantilever (106) will not be able to makesufficient electrical contact to the input transmission line (102).Hence the contact impedance will be high. In the case of a unwantedparticle (131) existing on a front surface of the input transmissionline (102) in the contact region (see FIG. 5(b)), the first movablecantilever (106) will not make a good contact with the inputtransmission line (102) regardless the dimension of the particle (130).

[0039] In addition to the effects of the unwanted particles, one mayneed to increase the contact pressure to ensure proper electricalcontact between a movable cantilever (106 or 107) and the inputtransmission line (102). For the flat cantilevers shown in FIG. 3, 4,and 5, the first and second movable cantilevers (106, 107) will make acontact to the input transmission line (102) without the presence ofunwanted particles. However, these contacts will be spread over a largearea. Furthermore, the movable cantilevers (106, 107) may make contactsto the substrate in areas outside the input transmission line (102). Insuch a case, the contact pressure for a fixed actuation force will besignificant reduced leading to poor electrical contacts.

[0040] In order to minimize the effects of the unwanted particles and toincrease the contact pressure in Double-throw Switch C (100), astructure with recess regions in the movable cantilevers (106, 107) isprovided. As shown in FIGS. 6(a) and (b), a first recess region (132) iscreated in the first movable cantilever (106) in area overlapping theinput transmission line (102) and a second recess region (133) iscreated in the second movable cantilever (107) in area overlapping theinput transmission line (102). Other parts of the Double-throw Switch C(100) are kept to be the same as the one described in FIGS. 3, 4, and 5.As shown in FIG. 6(b), a side-view taking along line F-F′ in FIG. 6(a),the height (134) of the recess regions (132, 133) is controlled duringthe fabrication and may be in the range from 1 to 20 μm. During theoperation, when the first movable cantilever (106) is actuated, theunwanted particle (130) on the substrate (101) will not get in touchwith the first movable cantilever (106). Hence, unlike in the case ofFIG. 5(a), the presence of the unwanted particles will not havesignificant effect on the operation of the Double-throw Switch C (100).Furthermore, since the contact area of the movable cantilevers (106,107) when actuated, is much less compared to the case without the recessregions (132, 133), the contact pressure will be increased even with thesame actuation force. With the recess regions (132, 133) in thecantilevers (106, 107), the contact resistance during the operation thenwill decrease.

[0041] The operation may be improved further by creating more than onerecess region in each movable cantilever. With a single recess region ineach movable cantilever, the movable cantilevers (106, 107) still canget in touch with the substrate (101) when actuated, leading to areduced pressure. To overcome this, two recess regions may be createdfor each movable cantilever as shown in FIGS. 7(a) and 7(b), across-sectional view of the switch taking along line G-G′ in FIG. 7(a).Here, it can be seen that in addition to the first recess region (132),a third recess region (135) has been created in the first movablecantilever (106). Whereas for the second movable cantilever (107), afourth recess region (136) has been created in addition to the secondrecess region (133). When actuated, the two recess regions for eachmovable cantilever will get in touch with the substrate (101) and theinput transmission line (102). Hence, the effects of unwanted particlescan be reduced and the pressure can be increased.

[0042] For the switching of microwave signals at very high frequencies,such as more than 10 GHz, it is required to have more uniform andstreamline distribution of the width of the microwave-propagating path,even in the transition region where the input transmission line makescontact with an actuated movable cantilever. One structure of thedouble-throw miniature microwave switch (140), having a tapered inputtransmission line (141) and two nonsymmetrical movable cantilevers, toachieve this is shown in FIG. 8(a). The first nonsymmetrical movablecantilever (142) connecting to a first output transmission line (143)has a protruding region (144) so that the inner angle (145) it makeswith the input transmission line (141) when actuated will not be abrupt.The second nonsymmetrical movable cantilever (146) connecting to asecond output transmission line (147) has a protruding region (148) sothat the inner angle (149) it makes with the input transmission (141)when actuated will not be abrupt. Furthermore, the corners (150, 151) ofthe input transmission line (141) are tapered. When the firstnonsymmetrical movable cantilever (142) is actuated to make electricalcontact with the input transmission line (141) and with the secondnonsymmetrical movable cantilever (146) being pushed away from the inputtransmission line (141), microwave signals will propagate from the inputtransmission line (141) through the contact region towards the firstoutput transmission line (143). Due to the smoothed inner angle (145)and the tapered corner (150) of the input transmission line (141), thereflection and losses for the propagating microwaves will be minimized.When the second nonsymmetrical movable cantilever (146) is actuated tomake electrical contact with the input transmission line (141) and withthe first nonsymmetrical movable cantilever (142) being pushed away fromthe input transmission line (141), microwave signals will propagate fromthe input transmission line (141) through the contact region towards thesecond output transmission line (147). Due to the smoothed inner angle(149) and the tapered corner (151) of the input transmission line (141),the reflection and losses for the propagating microwaves will beminimized.

[0043] Another structure of the double-throw miniature microwave switchto achieve this purpose is shown in FIG. 8(b). The switch (160) has aninput transmission line (161) with rounded corners and twononsymmetrical movable cantilevers. The first nonsymmetrical movablecantilever (162) connecting to a first output transmission line (163)has a protruding region (164) so that the inner angle (165) it makeswith the input transmission line (161) when actuated will have a roundedtransition and will not be abrupt. The second nonsymmetrical movablecantilever (166) connecting to a second output transmission line (167)has a protruding region (168) so that the inner angle (169) it makeswith the input transmission (161) when actuated will have a roundedtransition and will not be abrupt. Furthermore, the corners (170, 171)of the input transmission line (161) are rounded. When the firstnonsymmetrical movable cantilever (162) is actuated to make electricalcontact with the input transmission line (161) and with the secondnonsymmetrical movable cantilever (166) being pushed away from the inputtransmission line (161), microwave signals will propagate from the inputtransmission line (161) through the contact region towards the firstoutput transmission line (163). Due to the rounded inner angle (165) andthe rounded corner (170) of the input transmission line (161), thereflection and losses for the propagating microwaves will be minimized.When the second nonsymmetrical movable cantilever (166) is actuated tomake electrical contact with the input transmission line (161) and withthe first nonsymmetrical movable cantilever (162) being pushed away fromthe input transmission line (161), microwave signals will propagate fromthe input transmission line (161) through the contact region towards thesecond output transmission line (167). Due to the rounded inner angle(169) and the rounded corner (171) of the input transmission line (161),the reflection and losses for the propagating microwaves will beminimized.

[0044] For microwave switching applications, it is highly desirable tohave microwave switches with latching function so that the operatingpower can be minimized. Compared to miniature switches withelectrostatic actuation, it is more difficult to achieve latching in theelectromagnetically actuated counterparts. In another embodiment of thisinvention, an electromagnetically actuated switch with latching functionas shown in FIG. 9 is provided. In this figure, all numerals have thesame definition as those in FIG. 3 except for the items added to achievethe latching function, which are described as follows. As shownschematically in FIG. 9(a), this double-throw microwave switch (100L) isconstructed on a substrate (101), with an input transmission line (102),a first output transmission line (103), a second output transmissionlines (104) and a ground plane (105, in FIG. 9(b)). The first outputtransmission line (103) is connected to a first movable cantilever (106)through a first inclined potion (108) whereas the second outputtransmission line (104) is connected to a second movable cantilever(107) via a second inclined potion (109). In order to accomplish thelatching function, a layer of input permanent magnetic film (102 m, inFIG. 9(b)) is deposited under part of the input transmission line (102),a first cantilever permanent magnetic film (106 m) is deposited on partof the first movable cantilever (106), whereas a second cantileverpermanent magnetic film (107 m) is deposited on part of the secondmovable cantilever (107). In addition to the above-described items, athird non-movable cantilever (180) raised by a third inclined potion(181) is deposited with an anchor (182) attached to the substrate (101)to achieve the latching function. A third cantilever permanent magneticfilm (180 m) is deposited on top of the third non-movable cantilever(180). Width (102′) of the input transmission line (102), width (103′)of the first output transmission line (103), width (104′) of the secondoutput transmission line (104), width (106′) of the first movablecantilever (106) and width (107′) of the second movable cantilever (107)are selected to give proper microwave properties. It is thus understoodthat these widths (102′, 103′, 104′, 106′ and 107′) are selectedaccording to the thickness (101″, FIG. 9(b)) of the substrate (101), thedielectric constant of the substrate (101), the frequencies of operationand the characteristic impedance required. The third non-movablecantilever (180), the third inclined potion (181) and anchor (182) havethe same width (180′), which is selected to give reliable latchingeffects.

[0045] As shown in FIG. 9(b), a cross-sectional view taken along H-H′ inFIG. 9(a) details the relative positions of the input transmission line(102), the first output transmission line (103) with the first movablecantilever (106), the second output transmission line (104) with thesecond movable cantilever (107) and a third non-movable cantilever (180)for latching purpose. The vertical separation between the movablecantilevers (106, 107) and the input transmission line (102) is given by(110) while the overlaps between the movable cantilevers (106, 107) andthe input transmission line (102) are (113, 114, in FIG. 9(b)). Thethickness (103″) of the first movable cantilever (106) and the firstoutput transmission line (103), the thickness (106 m″) of the firstcantilever permanent magnetic film (106 m), the thickness (104″) of thesecond movable cantilever (107) and the second output transmission line(104), and the thickness (107 m″) of the second cantilever permanentmagnetic film (107 m) are selected so that the first movable cantilever(106) and the second movable cantilever (107) are sufficiently flexiblefor actuation and do not interfere with the propagating of microwavesignals. The thickness (180″) of the third non-movable cantilever (180)is selected so that the third non-movable cantilever (180) including thethird cantilever permanent magnetic film (180 m) is sufficiently rigidand will not deform significantly when an actuation force is applied.The thickness (180 m″) of the third cantilever permanent magnetic film(180 m) and the thickness (102 m″) of the input permanent magnetic film(102 m) are selected so that they can provide sufficient magnetic momentfor the latching function. As shown in FIG. 9(b), the permanent magneticfilms (102 m), (106 m), (107 m) and (180 m) are magnetized horizontallyand all in the same direction (pointing from N to S).

[0046] With the magnetization directions described above in mind, theoperation of the double-throw miniature electromagnetic switch (100L)with latching function can be described easily in FIG. 10. In FIG.10(a), the schematic cross-sectional view of the switch (100L) disclosedin FIG. 9 is shown for the case when a dc current is applied to theelectromagnet (120). Due to the magnetic flux (121) going through thefirst cantilever permanent magnetic film (106 m), the first cantileverpermanent magnetic film (106 m) will be attracted towards theelectromagnet (120), so that the leading end of the first movablecantilever (106) will get in touch with the input transmission line(102). Since the direction of the magnetic flux (122) going through thesecond cantilever permanent magnetic film (107 m) is opposite to thatexperienced by the first cantilever permanent magnetic film (106 m), thesecond cantilever permanent magnetic film (107 m) will experience arepulsion force and the second movable cantilever (107) will be pushedaway from the input transmission line (102) and get in touch with thethird non-movable cantilever (180).

[0047] Given the magnetization of the input permanent magnetic film (102m) and the first cantilever permanent magnetic film (106 m) and therelative position of the two permanent magnetic films (102 m, 106 m),when the first movable cantilever (106) is actuated and moved to be nearthe input transmission line (102), an attraction force is presentbetween the first cantilever permanent magnetic film (106 m) and theinput permanent magnetic film (102 m). The above attraction force willbe greater than the attraction force present between the firstcantilever permanent magnet film (106 m) and the third cantileverpermanent magnetic film (180 m) due to the distance difference. Hence,once actuated, the first movable cantilever (106) will be latched to theinput transmission line (102) even when the magnetic flux (121) from theelectromagnet (120) is switched off (see FIG. 10(b)). Similarly, due tothe magnetization of the second cantilever permanent magnetic film (107m) and the third cantilever permanent magnetic film (180 m) and therelative position of the two permanent magnetic films (107 m, 180 m),there will be an attraction force between the second cantileverpermanent magnetic film (107 m) and the third cantilever permanentmagnetic film (180 m) when the second movable cantilever (107) isactuated and moved to be near the third non-movable cantilever (180).The above force will be grater than the attraction force between thesecond cantilever permanent magnetic film (107 m) and the inputpermanent magnetic film (102 m) because of the distance difference.Hence, the second movable cantilever (107) will be latched to the thirdnon-movable cantilever (180) even when the magnetic flux (122) from theelectromagnet (120) is switched off (see FIG. 10(b)). Microwave signalsfrom the input transmission line (102) will be guided to the firstoutput transmission line (103) through the first movable cantilever(106) and will not be guided to the second output transmission line(104).

[0048] When the direction of the dc current to the electromagnet (120)is reversed, the magnetic flux (123, 124) will reverse as shown in FIG.10(c)). In this case, the first cantilever permanent magnetic film (106m) will experience a repulsion force and the first movable cantilever(106) will be pushed away from the input transmission line (102).Whereas the second cantilever permanent magnetic film (107 m) willexperience an attracting force and the second movable cantilever (107)will be attracted to make contact with the input transmission line(102). When the first movable cantilever (106) is actuated and moved tobe near the third non-movable cantilever (180), there will be anattraction force present between the first cantilever permanent magneticfilm (106 m) and the third cantilever permanent magnetic film (180 m).The above attraction force will be greater than the attraction forcepresent between the first cantilever permanent magnetic film (106 m) andthe input permanent magnetic film (102 m) because of the distancedifference. Due to the attraction force between the permanent magneticfilms (106 m, 180 m), after the new actuation, the first movablecantilever (106) will be latched to the third non-movable cantilever(180) even when the dc current to the electromagnet (120) is switchedoff (see FIG. 10(d)). During above actuation, the second cantileverpermanent magnetic film (107 m) will be attracted towards theelectromagnet (120). Therefore, the second movable cantilever (107) willmove towards the input transmission line (102). Due to the magnetizationof the second cantilever permanent magnetic film (107 m) and the inputpermanent magnetic film (102 m) and the relative position of the two(107 m, 102 m), there will be an attraction force between the secondcantilever permanent magnetic film (107 m) and the input permanentmagnetic film (102 m). The above force will be grater than theattraction force between the second cantilever permanent magnetic film(107 m) and the third cantilever permanent magnetic film (180 m). Hence,the second movable cantilever (107) will be latched to the inputtransmission line (102) even when the dc current to the electromagnet(120) is switched off (see FIG. 10(d)). Microwave signals from the inputtransmission line (102) will be guided through the second movablecantilever (107) to the second output transmission line (104) and willnot be guided to the first output transmission line (103).

[0049] In order to ensure low resistance contact between the inputtransmission line (102) and the movable cantilevers (106, 107), it ispreferable to create at least one recess region in the first movablecantilever (106) and to create at least one recess region in the secondmovable cantilever (107). In this way, the presence of any unwantedparticles between the movable cantilevers (106, 107) and the substrate(101) or between the movable cantilevers (106, 107) and the inputtransmission line (102) will not have a detrimental effect on theoperation. In addition, the pressure of contact between the inputtransmission line (102) and the movable cantilevers (106, 107) will beincreased.

[0050] The amount of overlaps (113, 114) is determined by the desiredminimum parasitic capacitances required for the overlapped regions whenmovable cantilevers (106, 107) are not in contact with the inputtransmission line (102). It is obvious that for fixed values ofseparation (110, in FIG. 9(b)) and widths (106′, 107′ in FIG. 9(a)) ofthe first and the second movable cantilevers (106, 107), the parasiticcapacitance values are directly proportional to the amounts of overlaps(113, 114). The amount of overlaps (113, 114) of the switch (100L) ispreferably to be as small as possible so that the effect of the overlaps(113, 114) on the frequencies of operation will be diminished. On theother hand, the amount of overlaps (113, 114) has to be large enough toensure good electrical contact between the movable cantilevers (106,107) and the input transmission line (102) and to ensure reliablelatching function. The latching separation (110L, in FIG. 10(d)) in thelatching state is much larger than the separation (110, in FIG. 9(b)) innormal position of the movable cantilevers (106, 107). Hence, theparasite capacitance of switch (100L) is expected to be smaller thanthat of the switch (100) without the latching function.

[0051] Although the miniature double-throw microwave switch (100L) withlatching function disclosed in FIGS. 9 and 10 is preferable, a latchingdouble-throw microwave switch without the third non-movable cantilever(180) is also feasible. In FIGS. 11(a) and 11(b), such a switch (100L′)is demonstrated with all numerals having the same definition as those inFIG. 3 except for the items added to achieve the latching function.Similar to the switch (100L) disclosed in FIGS. 9 and 10, switch (100L′)contains an input transmission line (102) with an input permanentmagnetic film (102 m), a first movable cantilever (106) with a firstcantilever permanent magnetic film (106 m) and connected to a firstoutput transmission line (103), a second movable cantilever (107) with asecond cantilever permanent magnetic film (107 m) and connected to asecond output transmission line (104). However, it does not contain athird non-movable cantilever. In FIG. 11(a) a schematic cross-sectionalview shows the miniature double-throw microwave switch (100L′) with a dccurrent applied to the electromagnet (120). Due to the magnetic flux(123) going through the first cantilever permanent magnetic film (106m), (106 m) will experience a repulsion force and the first movablecantilever (106) will be pushed further away from the input transmissionline (102). Since the direction of the magnetic flux (124) going throughthe second cantilever permanent magnetic film (107 m) is opposite tothat experienced by the first cantilever permanent magnetic film (106m), the second movable cantilever (107) will be attracted towards theinput transmission line (102) and the leading end of the second movablecantilever (107) will get in touch with the input transmission line(102). Due to the magnetization of the second cantilever permanentmagnetic film (107 m) and the input permanent magnetic film (102 m) andthe relative position of the two (107 m, 102 m), there will be anattraction force between the second cantilever permanent magnetic film(107 m) and the input permanent magnetic film (102 m). Hence, the secondmovable cantilever (107) will be latched to the input transmission line(102) even when the dc current applied to the electromagnet (120) isswitched off, as shown in FIG. 11(b). Without the magnetic flux (123),the first movable cantilever (106) will return to its normal positionwith a separation (110, in FIG. 11(b)) from the input transmission line(102). The attraction force between the input permanent magnetic film(102 m) and the first cantilever permanent magnetic film (106 m) aresmall due to the separation (110). Therefore the first movablecantilever (106) will not be attracted towards the input transmissionline (102). Microwave signals from the input transmission line (102)will be guided through the second movable cantilever (107) to the secondoutput transmission line (104) and will not be guided to the firstoutput transmission line (103).

[0052] Since the separation (110) of the switch (100L′) shown in FIG.11(b) is smaller than the latching separation (110L) of the switch(100L) shown FIG. 10(d), the switch (100L′) will have a larger parasiticcapacitance value than the switch (110L). It is obvious that for a fixedvalue of separation (110) and widths (106′, 107′, in FIG. 3(a)) of thefirst and the second movable cantilevers (106, 107), the parasiticcapacitance values are directly proportional to the amounts of overlaps(113, in FIG. 11(b)) and (114, in FIG. 11(a)). In order to reduce theparasitic capacitances, the amount of overlaps (113, 114) needs to be assmall as possible provided that a good electrical contact and a reliablelatching between the movable cantilevers (106, 107) and the inputtransmission line (102) are ensured.

[0053] It should be pointed out that for the miniature double-throwmicrowave switches described in FIGS. 9, 10, 11(a) and 11(b), thedirection of magnetization of the input permanent magnetic film (102 m),the first cantilever permanent magnetic film (106 m), the secondcantilever permanent magnetic film (107 m), and the third cantileverpermanent magnetic film (180 m) are selected to be the same and areparallel to the surface of the substrate (101). However, othermagnetization directions for the permanent magnetic films (102 m, 106 m,107 m and 180 m) could be chosen. FIGS. 11(c) and 11(d) give an exampleof a miniature double-throw microwave latching switch with magnetizationdirections different from those in FIGS. 9, 10, 11(a) and 11(b). In FIG.11(c), the input permanent magnetic film (102 m) is separated into twoparts: the first input permanent magnetic film (102 ma) and the secondinput permanent magnetic film (102 mb). The magnetization directions(indicated by arrows) of (102 ma) and (102 mb) are perpendicular to thesurface of the substrate (101) and are opposite to each other. Themagnetization directions of the first output permanent magnetic film(106 m) and the second output permanent magnetic film (107 m) are alsoperpendicular to the surface of the substrate (101) and are opposite toeach other (see arrows). Because the vertical component of the magneticfluxes (123, 124) at the top of the electromagnet (120) is along themagnetization direction of the first cantilever permanent magnetic film(106 m) and is opposite to that of the second cantilever permanentmagnetic film (107 m), the second movable cantilever (107) will beattracted towards the input transmission line (102) and the firstmovable cantilever (106) will be pushed further away from the inputtransmission line (102). Once the second movable cantilever (107) ispulled down by the external magnetic field to be close to the secondinput permanent magnetic film (102 mb), it will experience an attractionforce from (102 mb) due to the opposite magnetization direction.Therefore, the second movable cantilever (107) will be latched to theinput transmission line (102) even when the dc current to theelectromagnet (120) is switched off (see FIG. 11(d)). Due to a largedistance between the first cantilever permanent magnetic film (106) andthe first input permanent magnetic film (102 ma), the first movablecantilever (106) will not be attracted to the input permanent magneticfilm (102 ma). Microwave signals from the input transmission line (102)will be guided through the second movable cantilever (107) to the secondoutput transmission line (104) and will not be guided to the firstoutput transmission line (103).

[0054] Although for FIGS. 9, 10 and 11, an input permanent magnetic film(102 m) is deposited under the input transmission line (102), it shouldbe pointed out that the latching double-throw miniature microwaveswitches (100L, 100L′) could also be constructed with the inputpermanent magnetic film (102 m) deposited on top of the inputtransmission line (102).

[0055] In another embodiment of the invention, an electromagneticallyactuated double-throw microwave switch with a smooth transition regionbetween the input transmission line and the output transmission lines isprovided. As shown schematically in FIGS. 12(a) and 12(b), thismicrowave switch (190) is constructed on a substrate (191), with oneinput transmission line (192), a first output transmission line (193), asecond output transmission line (194) and a ground plane (195, in FIG.12(b)). The input transmission line (192) is connected to a movableinput cantilever (196) whereas the second output transmission line (194)is connected to a non-movable output cantilever (197). The first outputtransmission line (193) is deposited directly on the substrate (191).The width (192′) of the input transmission line (192), the width (196′)of the movable input cantilever (196), the width (193′) of the firstoutput transmission line (193), the width (194′) of the second outputtransmission line (194′) and the non-movable output cantilever (197) areselected to give a proper microwave properties. It is understood thatthese widths (192′, 193′, 194′ 196′) are selected according to thethickness (191″ in FIG. 12(b)) of the substrate (191), the dielectricconstant of the substrate (191), the frequencies of operation and thecharacteristic impedance required. As shown in FIG. 12(b), where anenlarged cross-sectional view of part of the transition region takenalong line J-J′ in FIG. 12(a) is given, the relative positions of theinput transmission line (192) and the movable input cantilever (196),the first output transmission line (193) and the non-movable outputcantilever (197) are presented. The thickness (192″) of the movableinput cantilever (196) and the input transmission line (192) is selectedto be substantially smaller than the thickness (194″) of the non-movableoutput cantilever (197) and the second output transmission line (194) sothat the non-movable output cantilever (197) is rigid whereas themovable input cantilever (196) is relatively flexible. The non-movableoutput cantilever (197) is made to be rigid so that it will not deformsignificantly when an actuation force is applied whereas the movableinput cantilever (196) is made to be relatively flexible so that it canmove upwards or downwards when an actuation force is applied. Thethickness of the first output transmission line (193) is given by (193″)in FIG. 12(b). A permanent magnetic film (198) is deposited on themovable input cantilever (196) and magnetized in such a way when anelectromagnet (199) is activated to generate magnetic flux (200, 201)there is an attracting force on the permanent magnetic film (198).Hence, the movable input cantilever (196) will be attracted towards thefirst output transmission line (193) and to make contact with it. Whenthe direction of the flux (200, 201) is reversed, there will be arepulsion force so that the movable input cantilever (196) will bepushed away from the first output transmission line (193) towards thenon-movable output cantilever (197) and to make contact with it. Hence,dependent on the position of the movable input cantilever (196),microwave signals applied to the input transmission line (192) canpropagate to either the first output transmission line (193) or thesecond output transmission line (194) through the non-movable outputcantilever (197), forming a double-throw microwave switch.

[0056] For the switching of microwave signals at very high frequencies,such as more than 10 GHz, it is required to have more uniform andstreamline distribution of the transmission lines, even in thetransition region where the actuated movable input cantilever (196)makes contact with the first output transmission line (193) and thenon-movable output cantilever (197). As seen in FIG. 12(a), thedisclosed double-throw microwave switch (190) has a smooth-outtransition region (202) and no sharp corner exists in this switch (190)Inside the contact area, the projection of the non-movable outputcantilever (197) overlaps the first output transmission line (193). Onceoutside the contact area, the output transmission lines (193, 194) startto split up and are separated by a variable distance (203), whichincreases gradually until reaching its maximum value (204). When themovable input cantilever (196) is actuated to make electrical contactwith the first output transmission line (193), microwave signals willpropagate from the input transmission line (192) through the transitionregion (202) towards the first output transmission line (193). Due tothe smoothed transition region (202), the reflection and losses for thepropagating microwaves will be minimized.

[0057] The amount of overlap (205, in FIG. 12(b)) between the movableinput cantilever (196) and the first output transmission line (193) isdetermined by the desired minimum parasitic capacitances required forthe overlapped region when the movable input cantilever (196) is not incontact with the first output transmission line (193). Similarly, theamount of overlap (206, in FIG. 12(b)) between the movable inputcantilever (196) and the non-movable output cantilever (197) isdetermined by the desired minimum parasitic capacitances required forthe overlapped region when the movable input cantilever (196) is not incontact with the non-movable output cantilever (197). The overlaps (205,206) of the switch are preferably to be small so that the effect of theoverlaps (205, 206) on the frequencies of operation will be minimized.On the other hand, the overlaps (205, 206) have to be large enough toensure good electrical contact between the movable input cantilever(196) and the first output transmission line (193), and between themovable input cantilever (196) and the non-movable output cantilever(197).

[0058] To add latching function to the microwave switch (190) disclosedin FIGS. 12(a) and 12(b), an input permanent magnetic film (196 m) isadded on the movable input cantilever (196), a first output permanentmagnetic film (193 m) on part of the first output transmission line(193), and a second output permanent magnetic film (197 m) on thenon-movable output cantilever (197), as shown in FIG. 12(c), where allnumerals having the same definition as those in FIGS. 12(a) and (b)except for the items added to achieve the latching function. It is notedthat the first output permanent magnetic film (193 m) could also bedeposited under the first output transmission line (193) and the secondoutput permanent magnetic film (197 m) could also be deposited under thenon-movable output cantilever (197). The input permanent magnetic film(196 m) forms part of the input cantilever (196) whereas the secondoutput permanent magnetic film (197 m) forms part of the non-movableoutput cantilever (197). The input permanent magnetic film (196 m), thefirst output permanent magnetic film (193 m) and the second outputpermanent magnetic film (197 m) are preferably magnetized simultaneouslyso that magnetization of (196 m, 193 m, 197 m) are substantially in thesame direction (indicated by N and S in FIG. 12(c)).

[0059] When the electromagnet (199) is activated to generate magneticflux (200, 201), there is an attracting force on the input permanentmagnetic film (196 m). Hence, the movable input cantilever (196) will beattracted towards the first output transmission line (193) and to makecontact with it. Due to the magnetization of the input permanentmagnetic film (196 m) and the first output permanent magnetic film (193m) and the relative position of the two, there will be a magneticattracting force between the input permanent magnetic film (196 m) andthe first output permanent magnetic film (193 m). This will result in alatching even when the dc current applied to the electromagnet (199) isdisconnected. Since there is a separation between the input permanentmagnetic film (196 m) and the second output permanent magnetic film (197m) when the movable input cantilever (196) is pulled to the first outputtransmission line (193), the attracting force between (196 m) and (197m) will be weaker than that between (196 m) and (193 m). When thedirection of the magnetic fluxes is reversed, there will be a repulsionforce so that the movable input cantilever (196) will be pushed awayfrom the first output transmission line (193) and towards thenon-movable output cantilever (197) and to make contact with it. Due tothe magnetization of the input permanent magnetic film (196 m) and thesecond output permanent magnetic film (197 m) and the relative positionof the two, there will be a magnetic attracting force between the inputpermanent magnetic film (196 m) and the second output permanent magneticfilm (197 m). This will result in a latching even when the dc currentapplied to the electromagnet (199) is disconnected. Since there is aseparation between the input permanent magnetic film (196 m) and thefirst output permanent magnetic film (193 m) when the movable inputcantilever (196) is pushed to the non-movable output cantilever (197),the attracting force between (196 m) and (193 m) will be much weakerthan that between (196 m) and (197 m). Hence, dependent on the positionof the movable input cantilever (196), microwave signals applied to theinput transmission line (192) can propagate to either the first outputtransmission line (193) or the second output transmission line (194)through the non-movable output cantilever (197), forming a double-throwmicrowave switch with latching mechanism. It is noted that in order toachieve a microwave switch with satisfactory performance, the magneticmoment of the first output permanent magnetic film (193 m) will have tobe close to that of the second output permanent magnetic film (197 m).This can be achieved by controlling the mass, geometry, magnetization ofthe first output permanent magnetic film (193 m) and the second outputpermanent magnetic film (197 m). The overlaps (205, 206) of the switch(190L) are preferably to be small so that the effect of the overlaps(205, 206) on the frequencies of operation will be minimized. However,the value of overlaps (205, 206) has to be large enough to ensure goodelectrical contact between the movable input cantilever (196) and thefirst output transmission line (193) and between the movable inputcantilever (196) and the non-movable output cantilever (197) and toensure reliable latching function.

[0060] In order to ensure low resistance contact between the movableinput cantilever (196) and the first output transmission line (193), itis preferable to create at least one recess region (207, in FIG. 12(d))in the movable input cantilever (196) with the tip of the recess region(207) facing down. In this way, the presence of fine particles betweenthe movable input cantilever (196) and the first output transmissionline (193) will not have a detrimental effect on the operation.Similarly, in order to ensure low resistance contact between the movableinput cantilever (196) and the non-movable output cantilever (197),which connected to the second output transmission line (194), it ispreferable to create at least one recess region (208, in FIG. 12(d)) inthe movable input cantilever (196) with the tip of the recess region(208) facing up. In this way, the presence of fine particles between themovable input cantilever (196) and the non-movable output cantilever(197) will not have a detrimental effect on the operation. In addition,because of the recess regions (207, 208) in the movable input cantilever(196), the pressure of contact between the movable input cantilever(196) and the first output transmission line (193) and between themovable input cantilever (196) and the non-movable output cantilever(197) will be increased.

[0061] The foregoing description is illustrative of the principles ofthe present invention. The preferred embodiments may be varied in manyways while maintaining the spirit of this invention. For instance, inaddition to microstrip structure, the double-throw switches and switcharrays may be fabricated in a form of coplanar waveguide (CPW), in aform of stripline or other structures. Therefore, all modifications andextensions are considered to be within the scope and spirit of thepresent invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A miniature double-throwelectromagnetically actuated microwave switch comprising: a dielectricsubstrate having at least one input transmission line, a first outputtransmission line and a second output transmission line deposited on afront surface of said dielectric substrate for propagating and routingof microwave signals; a first cantilever connected to said first outputtransmission line and with a projection overlapping at least a part ofsaid input transmission line; a second cantilever connected to saidsecond output transmission line and with a projection overlapping atleast a part of said input transmission line; a first permanent magneticfilm deposited on a part of a top surface of said first cantilever foractuating said first cantilever; a second permanent magnetic filmdeposited on a part of a top surface of said second cantilever foractuating said second cantilever; an electromagnetic coil under saiddielectric substrate for actuating said first cantilever and secondcantilever.
 2. A miniature double-throw electromagnetically actuatedmicrowave switch as defined in claim 1, further comprising means tosupply an electric current to said electromagnetic coil, magnitude ofsaid electric current is greater than a pull-down threshold current, toactuate said first cantilever, causing electric connection between saidinput transmission line and first output transmission line and tode-actuate said second cantilever, causing electric isolation betweensaid input transmission line and said second output transmission line.3. A miniature double-throw electromagnetically actuated microwaveswitch as defined in claim 1, further comprising means to supply areverse electric current to said electromagnetic coil, magnitude of saidelectric current is greater than a pull-down threshold current, toactuate said second cantilever, causing electric connection between saidinput transmission line and said second output transmission line and tode-actuate said first cantilever, causing electric isolation betweensaid input transmission line and first output transmission line.
 4. Aminiature double-throw electromagnetically actuated microwave switch asdefined in claim 1, wherein said first cantilever and second cantileverare selected from a group of a metal membrane, and a dielectric membranewith conducting coatings on both a front surface and a back surface. 5.A miniature double-throw electromagnetically actuated microwave switchas defined in claim 1, wherein said input transmission line and outputtransmission lines are patterned conducting thin films with thicknessbetween 0.5 μm and 10 μm.
 6. A miniature double-throwelectromagnetically actuated microwave switch as defined in claim 1,wherein said first cantilever has at least one recess regions, at leastone of said recess regions have projection overlapping said inputtransmission line, and said second cantilever has at least one recessregions, at least one of said recess regions have projection overlappingsaid input transmission line, to minimize effects of particles presentunder said first cantilever and second cantilever.
 7. A miniaturedouble-throw electromagnetically actuated microwave switch as defined inclaim 1, wherein end region of said input transmission line is taperedso that the outer angles made with said first cantilever and said secondcantilever are not abrupt, said first cantilever has an protrudingregion so that inner angle made with said input transmission line whenin contact is not abrupt, said second cantilever has an protrudingregion so that inner angle made with said input transmission line whenin contact is not abrupt.
 8. A miniature double-throwelectromagnetically actuated microwave switch as defined in claim 1,further comprising a permanent magnetic film on a portion of said inputtransmission line for latching of said first cantilever when actuatedand for latching of said second cantilever when actuated.
 9. A miniaturedouble-throw electromagnetically actuated microwave switch as defined inclaim 8, further comprising a non-movable third cantilever with a thirdpermanent magnetic film for latching of said first cantilever whende-actuated and for latching of said second cantilever when de-actuated.10. A miniature double-throw electromagnetically actuated microwaveswitch as defined in claim 1, further comprising a conducting film on abackside of said dielectric substrate.
 11. A miniature double-throwelectromagnetically actuated microwave switch with latching mechanismcomprising: a dielectric substrate having an input transmission linewith a movable cantilever; a first output transmission line; a secondoutput transmission line with a non-movable cantilever for propagatingand routing of microwave signals; an input permanent magnetic film on atleast part of said movable cantilever; a first output permanent magneticfilm on part of said first output transmission line for latching of saidmovable cantilever when actuated; a second output permanent magneticfilm on part of said second output transmission line for latching ofsaid movable cantilever when de-actuated; and an electromagnetic coilunder said dielectric substrate for actuating said movable cantilever.12. A miniature double-throw electromagnetically actuated microwaveswitch with latching mechanism as defined in claim 11, furthercomprising means to supply an electric current to said electromagneticcoil, magnitude of said electric current is greater than a pull-downthreshold current, to actuate said movable cantilever, causing electricconnection between said input transmission line and first outputtransmission line and electric isolation between said input transmissionline and second output transmission line.
 13. A miniature double-throwelectromagnetically actuated microwave switch with latching mechanism asdefined in claim 11, further comprising means to supply a reverseelectric current to said electromagnetic coil, magnitude of saidelectric current is greater than a push-up threshold current, tode-actuate said movable cantilever, causing electric isolation betweensaid input transmission line and first output transmission line andelectric connection between said input transmission line and secondoutput transmission line.
 14. A miniature double-throwelectromagnetically actuated microwave switch with latching mechanism asdefined in claim 11, wherein said movable cantilever has at least tworecess regions, at least one of said recess regions have projectionoverlapping said first transmission line, and at least one of saidrecess regions have projection overlapping said non-movable cantileverto minimize effects of unwanted particles present under and on saidmovable cantilever.
 15. A miniature double-throw electromagneticallyactuated microwave switch with latching mechanism as defined in claim11, further comprising a smooth transition region between said inputtransmission line and said first and second output transmission lines toavoid sharp corners.
 16. A miniature double-throw electromagneticallyactuated microwave switch with latching mechanism as defined in claim11, wherein said movable cantilever is selected from a group of a metalmembrane, and a dielectric membrane with conducting coatings on both afront surface and a back surface.
 17. A miniature double-throwelectromagnetically actuated microwave switch with latching mechanism asdefined in claim 11, further comprising a conducting film on a backsideof said dielectric substrate.